The invention relates generally to metal oxide ceramic films used in integrated circuits (ICs). More particularly, the invention relates to reducing diffusion of a mobile specie into the substrate.
Metal oxide ceramic materials have been investigated for their use in ICs. For example, metal oxide ceramics that are ferroelectrics or are capable of being transformed into ferroelectrics are useful due to their high remanant polarization (2Pr) and reliable long-term storage characteristics. Non-ferroelectric metal oxide ceramics, such as superconductors, have also been investigated.
Various techniques, such as sol-gel, chemical vapor deposition (CVD), sputtering, or pulsed laser deposition (PLD), have been developed for depositing ferroelectric films on a substrate. Such techniques, for example, are described, for example, Budd et al., Brit. Ceram. Soc. Proc., 36, p107 (1985); Brierley et al., Ferroelectrics, 91, p181 (1989), Takayama et al., J. Appl. Phys., 65, p1666 (1989); Morimoto et al., J. Jap. Appl. Phys. 318, 9296 (1992); and co-pending U.S. patent applications Ser. Nos. 08/975,087, titled xe2x80x9cLow Temperature CVD Process using B-Diketonate Bismuth Precursor for the Preparation of Bismuth Ceramic Thin Films for Integration into Ferroelectric Memory Devices,xe2x80x9d U.S. Ser. No. 09/107,861, titled xe2x80x9cAmorphously Deposited Metal Oxide Ceramic Films,xe2x80x9d all of which are herein incorporated by reference for all purposes.
Metal oxide ceramics are often treated with a post-deposition thermal process at a relatively high temperature in order to produce resulting materials with the desired electrical characteristics. For example, some Bi-based oxide ceramics such as strontium bismuth tantalate (SBT) are thermally treated by a xe2x80x9cferroanneal.xe2x80x9d The ferroanneal converts the as-deposited films into the ferroelectric phase. After the as-deposited films are converted into the ferroelectric phase, the ferroanneal continues, growing the grain size (e.g., greater than about 180 nm) of the films in order to achieve a good remanent polarization. Other types of metal oxide ceramics can be deposited as ferroelectrics. For example, lead zirconium titanate (PZT) is often deposited at a relatively higher temperature, such as greater than 500xc2x0 C., to form an as-deposited film with a ferroelectric perovskite phase. Although the PZT is deposited as a ferroelectric, a post-deposition thermal process is often still needed to improve its electrical characteristics.
Typically, the metal oxide ceramics comprise a mobile specie. The high temperature of the post-deposition heat treatment causes diffusion of the mobile specie out of the metal oxide ceramic layer. The amount of mobile specie that diffuses out of the metal oxide ceramic layer is referred to as an xe2x80x9cexcess mobile specie.xe2x80x9d The mobile specie can be in the form of atoms, molecules, or compounds. Diffusion of the excess mobile specie can have an adverse impact on yields. The excess mobile specie can easily migrate into other regions of the IC, such as the substrate, during the post deposition heat treatment. This can result in shorts and/or alter the electrical properties of other device regions, such as the diffusion regions.
As evidenced by the foregoing discussion, it is desirable to counteract the, adverse effects caused by diffusion of an excess mobile specie from a metal oxide ceramic layer.
The invention relates to metal oxide ceramic films and their applications in ICs. More particularly, the invention reduces the diffusion of an excess mobile specie from a metal oxide ceramic into the substrate.
In accordance with the invention, a barrier layer is provided. The barrier layer serves as a diffusion barrier to reduce or minimize the diffusion of the excess mobile specie. In one embodiment, the barrier layer is provided on a substrate separating the metal oxide ceramic and the substrate.
In one embodiment, the barrier comprises a material that reacts with the mobile specie. The reaction traps the mobile specie, preventing it from passing through the barrier layer. In another embodiment, the barrier layer comprises a dense material in order to inhibit the passage of the mobile specie. Also, a barrier layer comprising an amorphous material or a material with very small grain size is useful. Such materials extend the diffusion pathways of the mobile specie, making it more difficult for the mobile specie to diffuse through.
In another embodiment, the barrier layer comprises a grain surface having little or no attractive interaction with the mobile specie. Alternatively, a barrier comprising a grain surface having a strong interaction with the mobile specie and high activation energy for the mobile specie to migrate is also useful.
In yet another embodiment, the stoichiometry or composition of the metal oxide ceramic is selected to reduce or minimize diffusion of the mobile specie without adversely affecting the electrical properties of the material. Additionally, the deposition parameters of the metal oxide ceramic can be controlled to reduce the diffusion of the excess mobile specie from the metal oxide ceramic. In one embodiment, the ratio of oxidizer to the precursor amount of oxidizer is reduced to reduce diffusion of the mobile specie.